Automatic airfoil root prep machine and associated method

ABSTRACT

An apparatus for polishing an airfoil root includes a fixture for holding the airfoil, an actuation cylinder assembly for moving the fixture holding the airfoil, a brush, a motor for rotating the brush, a switch, and control circuitry. The actuation cylinder assembly is configured to move the fixture holding the airfoil toward the brush to trigger the switch, and the control circuitry is configured to run a timer when the switch is triggered to control contact between the airfoil and the brush for polishing.

BACKGROUND

The present invention relates to an apparatus and method for preparingairfoil roots through polishing or cleaning.

In many situations it is desirable to polish or otherwise clean orprepare a workpiece. For example, in some applications, portions ofairfoils for gas turbine engines are desired to be polished to removeoxidation to allow for electrical contact for a plating operation. Insuch situations, it is desired to remove oxidation to provide electricalcontact at a bottom of a root of the airfoil. The plating operation canthen be performed, such as for a Turbo Tip™ application where materialis plated onto a tip of the airfoil to facilitate cut-in seal formationat the airfoil tip when installed in a gas turbine engine.

In the prior art, polishing operations were performed manually with anoperator manually holding a blade root in contact with a rotatingpolishing brush. This manual process presents a number of ergonomic andsafety concerns because the operator must perform repetitive tasks andplace his or her hands near the rotating brush. Moreover, manualpolishing can result in undesirable variation between polishingoperations due to operator actions that are not identical for allpolishing operations.

Thus, an improved method an apparatus for workpiece polishing orcleaning is desired.

SUMMARY

An apparatus for polishing an airfoil root according to the presentinvention includes a fixture for holding the airfoil, an actuationcylinder assembly for moving the fixture holding the airfoil, a brush, amotor for rotating the brush, a switch, and control circuitry. Theactuation cylinder assembly is configured to move the fixture holdingthe airfoil toward the brush to trigger the switch, and the controlcircuitry is configured to run a timer when the switch is triggered tocontrol contact between the airfoil and the brush for polishing. Inanother aspect, the present invention includes an associated polishingmethod.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an airfoil polishing machine according tothe present invention.

FIG. 2 is a perspective view of the machine of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of an airfoil polishing machine 10, and FIG. 2is a perspective view of the machine 10. In the illustrated embodiment,the machine 10 includes a brush 12, a motor 14, a fixture 16, anactuation cylinder 18, a switch 20, a control valve 22, a limit switch24, control circuitry 26, operator controls 28, a hood 30, a proximitysensor 32 and a vent system 34. A workpiece 36 and an optional workpiecemask 38 can be engaged with the machine 10 for polishing, buffing,abrasive cleaning or other preparation procedures. As used herein, theterm “polishing” is intended to encompass all polishing, buffing,abrasive cleaning or other similar procedures.

The brush 12 can be an abrasive polishing brush, such as a 10 inch (25.4cm) outer diameter aluminum oxide grit wheel brush, available fromWeiler Corp., Cresco, Pa. The particular characteristics of the brush 12can vary as desired for particular applications. Moreover, inalternative embodiments, a polishing, buffing or cleaning implementother than a brush could be used. The motor 14 is used to rotate thebrush 12. In one embodiment, the motor is a 1 horsepower (746 watt)rotary buffer, available from Baldor Electric Co., Fort Smith, Ark.

The fixture 16 is used to movably hold the workpiece 36. In theillustrated embodiment, the fixture 16 includes a workpiece holder slot16-1 that can accept and retain the workpiece 36 (along with the mask38, if present) as well as a linear track 16-2 for guiding the workpiecealong a linear path that extends toward the brush 12.

The actuation cylinder 18 can be a fluidically-actuated cylinder thatproduces substantially linear actuation, such as a pneumatic cylinder ora hydraulic cylinder. Fluid can be supplied from a fluid supply 40through a suitable control valve 22 to pressurize the actuation cylinder18 to induce movement. The fluid supply 40 can be incorporated withinthe machine 10, or can be an external supply such as a pneumatic shopair system connected to the control valve 22 and the actuation cylinder18 through suitable conduits, hoses, pipes, etc. The fixture 16,specifically the holder 16-1, is engaged with the actuation cylinder 18such that the actuation cylinder can move the fixture (carrying theworkpiece 36) toward or away from the brush along the linear path.

The switch 20 is configured to sense when the fixture 16 has moved theworkpiece 36 to a given point sufficient to bring the workpiece 36 intocontact with the brush 12. When the switch 20 is triggered, a timer isactivated by the control circuitry 26 to regulate the cleaningoperation.

The limit switch 24 is configured to detect excessive movement of theholder 16-1 of the fixture 16 toward the brush 12 beyond a given point.The limit switch 24 is generally located closer to the brush 12 than theswitch 20. Triggering (i.e., “faulting out”) the switch 24 can indicatethat the brush 12 is worn or otherwise in need of replacement, or that aworkpiece 36 is not present in the fixture 16. Moreover, triggering theswitch 24 can generate a suitable indication to an operator via thecontrol circuitry 26 that action is needed.

The control circuitry 26 acts as the central control for most of thefunctions of the machine 10. The control circuitry 26 can includesuitable circuits, processors, memory and other subcomponents asnecessary or desired for particular applications. The operator controls28 are provided to allow an operator to activate and control the machine10. In one embodiment, the operator controls 28 include a pair ofoperator buttons, switches or other suitable controls for activating themachine 10 to perform a polishing operation, with the pair of operatorcontrols configured as “dead man” switches such that all (i.e., both)must be triggered to activate the machine 10 to perform a polishingoperation. In this way the operator controls 28 help ensure that anoperator must place both hands at the controls 28 and away from thebrush 12 during polishing, to promote operator safety. The operatorcontrols can include other functionality, such as suitable indicators ordisplays as desired.

The hood 30 can cover portions of the machine 10 during operation foroperator safety purposes and to help contain dust and debris. The hood30 can be pivotal, to allow access inside when needed. When closed, thehood 30 can cover the brush 12, the motor 14, and at least portions ofthe fixture 16, the workpiece 36 and the mask 38. The hood 30 caninclude an opening 30-1 to allow the workpiece 36 to be inserted intothe holder 16-1 of the fixture 16 with the hood 30 closed, and for theworkpiece 36 and the fixture 16 to be moved toward the brush 12 during apolishing operation while the hood 30 remains closed. The proximitysensor 32 can be positioned adjacent to the hood 30 to detect when thehood 30 is open. An open hood condition can be indicated to the controlcircuitry 26, and can prevent a polishing operation from beginning, thatis, operations of the motor 14 and the actuation cylinder 18 can beprevented and actuation of the operator control 28 overridden. The ventsystem 34 can be operably connected to the hood 30 to evacuate dust anddebris.

The machine 10 can be used with a variety of types of workpieces 36. Inone embodiment, the workpiece 36 is an airfoil for a gas turbine engine,and includes a root portion. The workpiece 36 can be made of anickel-based superalloy or other materials. The machine 10 can be usedto help remove oxidation from the workpiece, in particular to removeoxidation from a bottom portion of the root of an airfoil to allow forelectrical contact at the root for a later plating operation.

In order to perform a polishing operation, an operator can firstposition the mask 38, if used, on the workpiece 36. The workpiece 36 andthe mask 38 are then placed in the holder 16-1 of the fixture 16 (withthe root facing toward the brush 12 if the workpiece 36 is an airfoil),which is initially in a “home” position spaced from the brush 12 andaccessible from outside the hood 30. The hood 30 is closed if it isopen. The operator then triggers the operator controls 28 to initiatepolishing—the operator should not be touching the workpiece 36 at thispoint. The control circuitry 26 responds to the operator input byrotating the brush 12 with the motor 14. The actuation cylinder 18 movesthe fixture 16 and the workpiece 36 toward the rotating brush 12 alongthe linear path. The workpiece 36 (i.e., the root of the airfoil) comesinto contact with the rotating brush 12, which can abrasively removeoxidation on the workpiece 36. The actuation cylinder 18 advances thefixture 16 holding the actuation cylinder 18 the workpiece 36 toward thebrush 12 at given pressure within the actuation cylinder 18, such asapproximately 14 psi (96.53 kPa). The pressure within the actuationcylinder 18 can correspond to a force of the brush 12 against theworkpiece 36 of approximately 5-6 lbs (22.24-26.69 N) in someembodiments. When the actuation cylinder 18 moves the fixture 16 farenough the trigger the switch 20, a timer is initiated by the controlcircuitry 26. The control circuitry 26 governs operation of theactuation cylinder via the control valve 22, and maintains contactbetween the workpiece 36 and the brush 12 for a given time periodestablished by the timer, such as 1-2 seconds in one embodiment. In thisway, movement of the holder 16-1 and the workpiece 36 toward the brush12 is not to any particular fixed spatial location, but can correspondto a variety of spatial locations of the holder 16-1 and the workpiece36 relative to the brush 12. The actuation cylinder 18 will continue toadvance the fixture 16 as long as pressure is supplied to do so, withthe corresponding travel distance of the workpiece 36 able to varydepending upon factors such as the amount of wear of the brush 12. Thelimit switch 24 detects excessive movement of the fixture 16 which canindicate that the brush 12 is worn and in need of replacement. After thegiven time period, during which polishing is accomplished due toabrasive contact between the brush 12 and the workpiece 36, the controlcircuitry 26 caused the actuation cylinder 18 to move the fixture 16 andthe workpiece 36 away from the brush 12 and back to the home position.The operator can then remove the polished workpiece 36, and canoptionally insert a new workpiece to begin another polishing operation.The control circuitry 26 can let the motor 14 continue to run and rotatethe brush 12 after the fixture 16 has returned to the home position fora period of time, such as two minutes, to reduce on/off cycling of themotor 14 between successive polishing operations. Operation of the motor14 can be stopped during such a time period if the proximity sensor 32detects that the hood 30 has been opened.

Those of ordinary skill in the art will recognize that the presentinvention provides numerous advantages and benefits. For example,reliable and repeatable polishing can be provided despite brush wearover time that can reduce the diameter of the brush or variations inindividual workpieces. Moreover, the need for complex brush actuationequipment with complex positioning and sensors is reduced, which resultsin greatly reduced capital costs for the polishing equipment.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

1. An apparatus for polishing an airfoil root, the apparatus comprising:a fixture for holding the airfoil; an actuation cylinder assembly formoving the fixture holding the airfoil; a brush; a motor for rotatingthe brush; a switch, wherein the actuation cylinder assembly isconfigured to move the fixture holding the airfoil toward the brush totrigger the switch; and control circuitry, wherein the control circuitryis configured to run a timer when the switch is triggered to controlcontact between the airfoil and the brush for polishing.
 2. Theapparatus of claim 1, wherein the actuation cylinder assembly comprisesa linear pneumatic cylinder.
 3. The apparatus of claim 1 and furthercomprising: a limit switch configured to detect excessive travel of thefixture indicative of brush wear or the absence of the airfoil in thefixture.
 4. The apparatus of claim 1 and further comprising: a hood forshielding at least the brush during operation.
 5. The apparatus of claim4 and further comprising: a proximity sensor for detecting whether thehood is open.
 6. The apparatus of claim 1 and further comprising: a pairof operator controls for activating the apparatus to perform a polishingoperation, wherein the pair of operator controls are configured suchthat all must be triggered to activate the apparatus to perform apolishing operation.
 7. The apparatus of claim 1, wherein the actuationcylinder is pressurized at approximately 96.53 kPa (14 psi) to advancethe fixture.
 8. The apparatus of claim 1, wherein timer is configured torun to a time period of approximately 1-2 seconds before the actuationcylinder moves the fixture away from the brush, wherein the actuationcylinder continues to advance the fixture toward the brush during thetime period of the timer.
 9. The apparatus of claim 1 and furthercomprising: a vent system for venting airborne material present duringoperation of the apparatus.
 10. The apparatus of claim 1 and furthercomprising: a mask for masking a portion of the airfoil duringpolishing.
 11. A method of polishing a workpiece, the method comprising:positioning the workpiece in a fixture, wherein the fixture is movable;rotating a brush; moving the fixture toward the rotating brush at agiven pressure in the actuation cylinder so that the workpiece cancontact the brush; triggering timer when a position of the fixturereaches a given point relative to the rotating brush; and moving thefixture away from the rotating brush with the actuation cylinder after atime period of the timer has elapsed.
 12. The method of claim 11,wherein time period of the timer is approximately 1-2 seconds.
 13. Themethod of claim 11, wherein operation of the actuation cylindercontinues to advance the fixture toward the brush during the time periodof the timer.
 14. The method of claim 13, wherein a pressure in theactuation cylinder to move the fixture toward the rotating brush isapproximately 96.53 kPa (14 psi).
 15. The method of claim 11, whereinthe brush is rotated for at least 2 minutes when activated to reducemotor cycling between polishing operations.
 16. The method of claim 11and further comprising: detecting a movement limit of the fixturerelative to the rotating brush, to detect excessive movement of thefixture.